A particle (charge +40 mu C) is located on the x axis at the point x=-20, and a second particle (charge -50 muC) is also on x axis x=30. What is the magnitude of the total electrostatic force on a third particle (charge-=4 muC) placed at origin x=0

Question

A particle (charge +40 mu C) is located on the x axis at the point x=-20, and a second particle (charge -50 muC) is also on x axis x=30.  What is the magnitude of the total electrostatic force on a third particle (charge-=4 muC) placed at origin x=0

anonymous · Answer

I have began the question and I believe we'll be using the equation F2=q1q2/r^2

and then use the superposition principle

this is what I have so far, but I get the wrong answer.. what am I doing wrong?

anonymous · Answer

my work for this problem being the bottom half portion..

anonymous · Answer

OH.. I have a correction to put on the problem statement.  Particle 3 located on origin has the charge of -4muC

anonymous · Answer

It's another very similar problem. Same concept just different values.  From what I realized on this problem was that I forgot the direction of the Force in the x direction.. I figured it out later on.. and obtained the correct answer...

anonymous · Answer

i've done the problem again.. I didn't change anything except the input in the calculator-parenthesis are important.. I also added the cos(180) to both since the direction of the force for particle 3 is to the left.. 

For F13=35.95N
F23=-19.97N
then I add them up..16.01

the answer should be 56 according to the answer sheet.. which If both were positive I'd add them and get 55.922.. 

so I must have a sign wrong somewhere